Development Of Novel Chemically Modified Electrodes And Its' Applications In The Environmental And Biological Analysis

Environmental science, life science and materials science are dominating the 21st century, all the basic studies and high-tech development in these scientific area need the support of the analytical science, which brought forward new challenges to it. Based on the chemically modified electrodes as chemo/biosensors, electrochemical voltammetry has several advantages in that the instrument is simple and suitable for constructing inexpensive and portable detectors, which aroses the research workers'attentions. In this thesis, a series of studies on the development of novel modified electodes as chemo/biosensors and their application in the analysis in environmental and biological area, and some valuble results were obtained. The main points of this thesis are summarized as follows:1. Biocompatible aurum (Au) nanoparticle-structured supported bilayer lipid membrane (sBLM) modified with anionic sites was developed for the detection of cytochrome c (cyt c). Au nanoparticles were directly deposited through sBLM which modified with lauric acid to build a hybrid device of nanoscale electrode array via potential cycling in 10 mM HAuCl4 solution containing 0.1 M KCl. The properties of Au nanoparticle-doped sBLM composite were then characterized by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. Results indicated that Au nanoparticles grew in voids of the sBLM with size around 20-30 nm. With square wave voltammetry, after optimization, the results of the experiments indicate that the currents of cyt c were linear functions of its concentrations over the range from 1.0×10-7 M to 3.2×10-6 M and the limit of detection (LOD, S/N = 3) was 5×10-8 M. The influences of several common base pairs, amino acids and metal ions on determination of cyt c via this Au nanoparticle-doped sBLM composite were relatively low in experiments, suggesting the excellent biocompatibility of this detection method.2. Taking advantages of the larger specific surface area of single-walled carbon nanotubes and the lower contact resistance of–NH–C than that of multiple-walled carbon nanotubes and that of–S–Au, respectively, a ethylenediamine monolayer modified glassy carbon electrode (GCE) grafted by non-covalent and covalent sulphydryl groups jointly modified single-walled carbon nanotubes for arsenic(III) detection was developed. The resistance of ethylenediamine monolayer modified GCE was examined by electrochemical impedance spectroscopy. The characters of the non-covalent sulphydryl groups and the organized non-covalently modified single-walled carbon nanotubes were examined by detecting arsenic(III) and atomic force microscopy, respectively. After end-capped the remaining carboxylic groups of single-walled carbon nanotubes by covalent sulphydryl groups, the last electrode was applied to detect arsenic(III) and a limit of detection (LOD) (S/N = 3) of 0.008μg L-1 was obtained. And also, common contaminants at levels presenting in natural water did not interfere with the assay.3. Based on layer-by-layer assembled DNA-functionalized single-walled carbon nanotube hybrids, a DNA biosensor for the detection of arsenic(III) in a nearly physiological pH environment was developed. The character of the DNA-functionalized single-walled carbon nanotube hybrids was examined by atomic force microscope. The redox process between arsenic(III) and arsenic(0) on the biosensor was proved. The growth of those hybrids on glassy carbon electrode was monitored by detecting arsenic(III). The arsenic(III) current on the biosensor was similar over a broad pH range (3.0 - 8.0) and the limit of detection (S/N = 3) was 0.05μg L-1 at pH 7.0. The biosensor can be reused up to 16 times.4. GCEs modified with DNA-functionalized single-walled carbon nanotube hybrids by layer-by-layer was developed for the detection of 2,4,6-trinitrotoluene. The character of the DNA-functionalized single-walled carbon nanotube hybrids was examined by atomic force microscope. Compared with single-walled carbon nanotubes- alone modified electrode, DNA-functionalized single-walled carbon nanotube hybrids-modified one exhibited the more superior ability of detecting 2,4,6-trinitrotoluene, including the higher sensitivity and the lower overpotentials, due to plenty ofπ-electrons and hydrogen bond binding sites were provided. This modified electrode showed a fast response towards 2,4,6-trinitrotoluene and the detection could be finished within 15 s. A limit of detection of 0.5μg L-1 was obtained by this modified electrode with a linear range at least up to 800μg L-1. Stability test showed an average relative standard deviation of 3.5% for 40 consecutive runs with a same modified electrode and the reproducibility of the responses of 2,4,6-trinitrotoluene was within 5.1% from one electrode preparation to another (n = 10). And also, the applicability of this modified electrode was demonstrated for the analysis of 2,4,6-trinitrotoluene in spiked groundwater.5. A novel carbon nanotubes (CNTs) film-modified electrode was developed by controllable adsorption of the CNTs onto the monolayer of dodecylamine chemically GCE based on hydrophobic forces. The electrochemical characteristics of the dodecylamine monolayer-modified GCE were examined by electrochemical impedance spectroscopy and cyclic voltammetry. Compared with the self-assembled monolayer of dodecanethiol-modified gold electrode, the prepared dodecylamine monolayer-modified GCE presented the smaller resistance and the higher capacitance. In addition, after SWCNTs were controllably adsorbed onto the both modified electrodes by hydrophobic forces, the dodecylamine monolayer-modified GCE showed a larger capacitance than that of bare GCE for its small resistance and good conductivity of CNTs, but the SAM of dodecanethiol-modified gold electrode was failed to achieve the same result. Furthermore, the proposed SWCNTs dodecylamine monolayer-modified GCE was successfully used to determine dopamine in the presence of ascorbic acid after the adsorption of ssDNA.6. Based on theπ–πelectron interaction, ssDNA were adsorbed onto single-walled carbon nanotubes- (SWCNTs-) modified electrode, without the assistance of utrasonic. The characters of this modified electrode were determined by cyclic votammetry and scanning electron microscopy. Compared with SWCNTs- alone modified electrode, this jointly modified electrode exhibited the more superior ability of electrocatalysis of dopamine, for the plenty of functional groups in DNA, such as amino groups and carbonyl groups. The modified electrode was used to selectively detect dopamine in the presence of ascorbic acid, a limit of detection (S/N = 3) of 0.4μM was obtained with a linear range at least up to 30μM.